Statistical communication link

ABSTRACT

A communications system ( 34 ) that monitors a state of a plurality of radios ( 10 ). In one embodiment, the communications system ( 34 ) automatically and continuously monitors the number of radios ( 10 ) tuned to each of a plurality of available radio stations. Each radio ( 10 ) generates a coded signal depending on which radio station the radio ( 10 ) is currently tuned to. The coded signal is applied to a frequency generator ( 32 ) that generates a unique frequency signal for each code that is then transmitted by the radio ( 10 ). Each radio ( 10 ) tuned to the same station would transmit the same unique frequency signal at substantially the same power level. The frequency signals transmitted by all of the radios ( 10 ) are received by a receiver ( 34 ), such as a satellite-based receiver ( 34 ), that separates the signals by frequency. The power received for each different frequency signal is then measured to give a total power output for that frequency. An estimation of the number of transmission for each different frequency signal is determined as the measured power level minus the expected receiver noise power, divided by the expected received power from a transmission from a single radio ( 10 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a communications system fordetermining a state of a transmitter and, more particularly, to acommunications system for providing an estimation of the number ofradios tuned to each of a plurality of radio stations, where the systemdoes not specifically identify a particular radio.

2. Discussion of the Related Art

Digital audio radio systems (DARS) that generate compressed digitalaudio signals to be transmitted by a digital audio transmission sourceand reproduced in a receiver associated with the DARS are known in theart. Audio signals to be broadcast by the DARS are generated in abroadcast studio and then converted to digital data. The digital dataradio signals are then sent to an earth based ground transmissionstation to be transmitted to a plurality of receivers within a receptionarea, or to be transmitted to one or more satellites orbiting the earthin a geosynchronous orbit. The satellites then transmit the digitalradio signals to a defined reception area over the Earth. U.S. Pat. No.5,592,471 issued to Briskman, Jan. 7, 1997, discloses a digital radiosystem of this type.

For DARS that use satellite communications, the compressed digital datais sent to the earth based ground station for transmission to one ormore satellites on a radio frequency “uplink” carrier. The satellitereceives the uplink signals from the ground station and thenre-transmits the signals to a defined area on the earth's surface whereradio reception is desired. For example, the satellite can have a“downlink” beam pattern that covers the continental Untied States. Thereceiver receives the downlink signal, decompresses it, and converts itback to an analog signal for both stereo channels using adigital-to-analog converter (DAC) for subsequent amplification andlistening through speakers.

It would be highly valuable if radio station personnel, marketinganalysts, potential advertisers and the like could automatically andreadily obtain information concerning the number of radios that aretuned to the several available radio stations that are broadcastingradio signals at different times of the day. In other words, specificinformation concerning how many listeners are listening to a particularradio station at any given time would be valuable for advertisingpurposes. Currently, no practical technique exists for automaticallydetermining what station a radio receiver is tuned to. Marketingpersonnel typically assess this information by specifically askingconsumers what stations they listen to through questionnaires, surveysand the like. Obviously, this technique is limited in its accuracy, andthe number of radio listeners able to be surveyed. A much better andmore accurate surveying technique would be provided if the individualradios themselves transmitted a unique coded frequency based on theparticular station that the receiver was tuned to, that was received anddeciphered by a receiver.

It is possible to equip each radio with a conventional transmitter thattransmits its own unique signal to identify which station the radio iscurrently tuned to. The individual radios could be separately identifiedbased on different coding schemes, such as frequency division multipleaccess (FDMA), time division multiple access (TDMA), or code divisionmultiple access (CDMA), known to those skilled in the art. For an FDMAimplementation, each radio would require its own unique frequencyspectrum to identify each individual radio and the station it is tunedto. However, because there would probably be millions of radio beingmonitored at a time, each having its own unique frequency spectrum, anidentification system of this type would not be feasible because of thelarge amount of bandwidth required. Similarly for both CDMA and TDMAimplementations, each radio would require its own unique code and timeslot, respectively. As with FDMA, CDMA and TDMA each require bandwidthin proportion to the number of communication links being transmitted.For the satellite DARS discussed above, bandwidth is at a premium.Because it is only necessary to provide an overall measurement of theaverage listenership per station, systems which identify the specificradio provide more information than is necessary for ratings purpose.

For a ratings service system to be feasible, it would need to identifythe number of radios tuned to the particular radio stations in a morepractical and cost effective manner than that discussed above. It istherefore an object of the present invention to provide a technique fordetermining a state of a transmitter without the need to provide eachtransmitter with its own unique frequency or code signal.

SUMMARY OF THE INVENTION

In accordance with the teachings of the present invention, acommunications system is disclosed that automatically and continuouslymonitors a state of a group of transmitters. In one embodiment, thecommunications system monitors the number of radios tuned to each of aplurality of available radio stations. Each radio generates a codedsignal depending on which radio station the radio is currently tuned to.The coded signal is applied to a frequency generator that generates aunique frequency signal for each code that is then transmitted by theradio. Each radio tuned to the same station would transmit the sameunique frequency signal at substantially the same power level.

The frequency signals transmitted by all of the radios are received by areceiver, such as a satellite based receiver, that separates the signalsby frequency. The power received for each different frequency signal isthen measured to give a total power output for that frequency. Anestimation of the number of transmissions for each different frequencysignal is determined as the measured power level minus the expectedreceiver noise power, divided by the expected received power of atransmission from a single radio. Therefore, an estimation of the numberof radios tuned to each radio station being monitored can be obtained.

Additional objects, advantages and features of the present inventionwill become apparent from the following description and appended claims,taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a radio incorporating a transmission systemfor transmitting a carrier wave frequency signal identifying whichstation the radio is currently tuned to, according to an embodiment ofthe present invention;

FIG. 2 is a block diagram of a communications system incorporating aplurality of the radios shown in FIG. 1, according to the invention; and

FIG. 3 is a graph depicting a power spectrum for determining whichradios are tuned to what frequency in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following discussion of the preferred embodiments directed to acommunications system for determining the number of radios currentlytuned to each of a plurality of different radio stations is merelyexemplary in nature, and is in no way intended to limit the invention orits applications or uses. For example, the discussion below is concernedwith identifying the number of radios tuned to the available radiostation at a given time. However, the teachings of the invention have amuch wider application in that it can determine many states of atransmitter by the same technique.

FIG. 1 shows a block diagram of a radio 10, such as a vehicle radio,that incorporates a system for transmitting a unique carrier frequencysignal depending on which radio station the radio 10 is currently tunedto. The radio 10 includes an AM antenna 12 that collects and tunes AM(amplitude modulated) radio frequency signals, and sends the signals toan AM tuner 14 that filters and tunes a particular AM frequencybandwidth from an AM radio station. Additionally, the radio 10 includesan FM antenna 16 that collects and tunes FM (frequency modulated) radiofrequency signals, and sends the signals to an FM tuner 18 that filtersand tunes a particular FM frequency bandwidth from an FM radio station.The part of the radio 10 using the antennas 12 and 16, the AM tuner 14and the FM tuner 18 are for conventional land-based radios, known in theart. Also, the radio 10 includes a satellite receive/transmit antenna 20that receives satellite radio signals from a satellite (see FIG. 2), andsends the signals to a satellite tuner 22 that filters and tunes aparticular frequency bandwidth from a satellite station. The satelliteantenna 20 and the satellite tuner 22 can be the type used inassociation with a DARS referred to above, in combination with theconventional land-based AM and FM radio. The antenna 20 is also used totransmit a unique carrier frequency signal to the satellite based onwhich station the radio 10 is currently tuned to as will be describedbelow. The tuners 14, 18 and 22 can be any type of suitable tuner for aparticular heterodyne and/or satellite DARS known in the art.

The radio 10 includes a user interface 26 that allows he user of theradio 10 to select which station he desires to listen to for all of theavailable AM, FM and satellite stations. Depending on which station isselected, the interface 26 sends a selection signal to each of thetuners 14, 18 and 22, which causes the appropriate tuner that isselected to output a signal to an audio generation system 28. The audiogeneration system 28 takes the particular frequency or encoded signalfrom the selected tuner 14, 18 or 22, and generates an audio signal thatis then applied to the radio speakers (not shown) for listening. Thedepiction of the tuners 14, 16 and 22, the user interface 26, and theaudio generation system 28 is in a simplistic form for discussionpurposes.

The selection signal from the user interface 26 is also applied to acarrier wave frequency determination system 30, according to theinvention. Based on which station the user selects by the user interface26, the carrier wave frequency system 30 will provide an output signalidentifying that selection to a carrier wave generator 32. The carrierwave generator 32 then generates a unique carrier wave frequency forthat particular output from the system 30. Each selected radio stationthat is being monitored has its own unique identification code in thefrequency determination system 30, and each identification code has itsown unique carrier wave frequency that is generated by the carrier wavegenerator 32. The carrier wave is applied to the antenna 20 where it istransmitted to the satellite. In one embodiment, each radio 10 tuned tothe same station would transmit the same unique frequency signal atsubstantially the same power level. A frequency reference signal isapplied from the satellite tuner 22 to the carrier wave generator 32 toalign the carrier wave frequency with the receiver in the satellite sothat various carrier wave frequencies identifying the individualstations can be more closely spaced, as would be understood to thoseskilled in the art.

Depending on which radio station the user selects, whether it be an AMstation, an FM station, or a digital satellite broadcast station, theradio 10 will transmit a unique carrier wave frequency identifying thestation. In general, if a transmitter (radio 10) is in state k out of apossible n states, it transmits a low power carrier tone at frequencyf_(k), where n distinct frequencies f₁-f_(n) are defined in theavailable spectrum. The carrier can be transmitted periodicallydepending on the particular application to conserve resources. Thecarrier wave transmitted by the radio 10 is received by a satellite inone embodiment. However, the use of a satellite to receive the stateinformation from the radio 10 is by way of a non-limiting example, inthat a ground-based receiver can also be used to receive the stateinformation from the radio 10. Since each radio 10 will transmit acarrier wave, the narrowness of the carrier wave spectrum required isonly limited by the stability and accuracy of generation of thetransmission frequency, and by the rate that each radio 10 changesbetween states. Thus, for a large number of radios 10, the required bandwidth for this scheme is negligible compared to the bandwidth necessaryto support large numbers of individual communication links.

For a practical application, the carrier wave generator 32 will provide20-30 different carrier wave frequencies, one for each of the stationsbeing monitored. The carrier wave generator 32 will generate frequencysignals in the 2-3 GHz range, where each frequency signal has abandwidth of about 1 kHz to separate the different carrier wavefrequencies. If one of the radios 10 is turned off, it will stop sendingthe particular carrier wave, and thus the power contribution from thatradio 10 will stop, and the overall transmitted power from all of theradios will decrease. Likewise, if the user selects a different radiostation, the carrier wave transmitted by that radio will change, and theoverall power for one frequency will decrease and the overall power foranother frequency will increase.

FIG. 2 shows a diagram of a communications system 34 of the inventionfrom the satellite perspective, according to the invention. A satellite36 orbiting the Earth 38 monitors a certain predefined reception area onthe Earth 38. A plurality of radio receiver locations 40 are depicted onthe Earth 38, where each location 40 represents a radio 10. Eachlocation 40 is designated with a frequency f₁, f₂, or f₃ as the carrierwave generated by the carrier wave generator 32 for that radio 10. Onlythree frequencies are shown for discussion purposes. Of course, in apractical application, the satellite 36 will monitor many more thanthree different frequencies and many more locations 40 (possiblymillions of locations) will be transmitting signals. The satellite 36would also transmit the radio signals received by the antenna 20 anddeciphered by the tuner 22.

The satellite 36 receives the carrier wave frequencies f₁-f₃ from theradio 10. All of the carrier wave frequencies f₁ combine to give acertain power contribution for that frequency, all of the carrier wavefrequencies f₂ combine to give a power contribution for that frequency,and all of the carrier wave frequencies f₃ combine to give a poweroutput for that frequency. Since all of the radios 10 emit the carrierwaves at substantially the same power level, each contribution to thetotal power from each radio 10 is about the same.

The satellite 36 includes a first frequency bin filter 42 that onlypasses the carrier wave signals at frequency f₁, a second frequency binfilter 44 that only passes the carrier wave signals at frequency f₂, anda third frequency bin filter 46 that only passes the carrier wavesignals at frequencies f₃. The filters 42-46 can be any suitable narrowbandpass filter known to those skilled in the art that effectivelypasses the signals in the bandwidth of interest. In this depiction, manycarrier waves arrive at each frequency bin filter 42-46, and will bephase incoherent relative to each other. Therefore, a measurement of thetotal power in each frequency bin will be proportional to the number oftransmitters transmitting in that frequency bin, and is thus a measureof the number of transmitters in the state associated with thatfrequency bin.

By measuring the total power output from each frequency bin filter42-46, an estimate of the number of radios 10 transmitting eachfrequency f₁-f₃ can be provided, and thus the number of radios tuned toa given station can be obtained. To do this, the output from the filter42 is applied to a power detector 48, the output of the filter 44 isapplied to a power detector 50, and the output of the filter 46 isapplied to a power detector 52. The power detectors 48-52 provide ameasurement of the power received by the satellite 36 at the particularbandwidth passed by each of the filters 42-46. In one embodiment, thepower detectors 48-52 are square law power detectors, known to thoseskilled in the art. However, any kind of power detector suitable fordigital or analog power detection of the type described herein can beused in accordance with the teachings of the present invention.

The power detection signal from each of the power detectors 48-52 isthen applied to a processor 54 that converts the analog power signal toa digital signal, and provides an estimation of the number oftransmissions for each frequency f₁-f₃. In one embodiment, theestimation of the number of transmissions at each frequency f₁-f₃ isbased on the expected receiver noise power and the expected receivedpower of a single transmission from a radio 10. In other words, becausethe noise of the receiver processing the frequency signal is known, andthe power of each carrier frequency transmission from each radio 10 isknown, the number of transmissions at each frequency f₁-f₃ can becalculated. In the processor 54, the expected receiver noise power issubtracted from the measured power level at each frequency, and thendivided by the expected received power from a single transmitter to givethe number of transmissions at each frequency f₁-f₃. FIG. 3 shows agraph of how the estimation of the number of the transmissions for eachfrequency is made according to one embodiment of the invention. Each ofthe frequencies f₁, f₂, and f₃ is depicted on the horizontal axis, andthe power detected at each frequency is depicted on the vertical axis.Each separation of power is based on the receiver noise N₀. If no radio10 is transmitting a particular carrier wave frequency, then the totaloutput power at that frequency would be N₀. In this representation,twelve radios 10 are transmitting at carrier wave frequency f₁, sixteenradios 10 are transmitting at carrier wave frequency f₂, and four radios10 are transmitting at carrier wave frequency f₃. Based on the power foreach transmission, each power contribution from each radio 10 at aparticular frequency is known to be one-quarter of N₀. Therefore, thetotal power output contribution for twelve radios transmitting atfrequency f₁ is 4N₀, the total power output for sixteen radiostransmitting at frequency f₂ is 5N₀, and the total power output for fourradios transmitting at frequency f₃ is 2N₀. As the number of radiostransmitting at the various frequencies changes over time, the totalpower output at each frequency f₁-f₃ will change accordingly based onthe noise N₀. The satellite 36 can download the information concerningthe number of radios tuned to a particular station to a ground basedstation (not shown) along with the normal telemetry information from thesatellite 36 that gives the satellite's vital information.

The transmit power required for each radio 10 can be determined from thedesired accuracy in counting the number of transmissions in each state.It is not necessary in the scheme of the invention to have sufficientpower for a single transmitter to be detectable. This would have beenhave necessary if individual communications were employed. For example,consider a case where the uncertainty in the number of transmitters in aparticular state can be as many as one hundred transmissions. Thetransmit power can then be set so that the received power from one radio10 is roughly {fraction (1/100)}th of the noise power in the detector.

The foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. One skilled in the art wouldreadily recognize from such discussion, and from the accompanyingdrawings and claims, that various changes, modifications and variationscan be made therein without departing from the spirit and scope of theinvention as defined in the following claims.

What is claimed is:
 1. A communications system for determining a stateof a plurality of radios, each radio transmitting one of a plurality ofunique signals based on the state of the particular radio, saidcommunications system comprising a receiver system receiving the uniquesignals, said receiver system separating the unique signals from theplurality of radios and measuring the combined power for each group ofseparated unique signals, said receiver system determining the number ofradios transmitting each unique signal based on the combined power. 2.The system according to claim 1 wherein the state is a radio stationthat the radio is currently tuned to.
 3. The system according to claim 1wherein the signals are carrier wave signals, where each carrier wavesignal has a predetermined center frequency.
 4. The system according toclaim 1 wherein the receiver system is a satellite based receiver systemon a satellite orbiting the earth.
 5. The system according to claim 1wherein the receiver system includes a plurality of narrow band passfilters, where each band pass filter passes one of the plurality ofunique signals, and a plurality of power detectors for detecting thepower output from each of the band pass filters.
 6. The system accordingto claim 1 wherein the receiver system provides an estimate of thenumber of radios transmitting each unique signal based on the combinedpower of each group of separated signals, the expected noise power inthe receiver system, and the expected received power from a singletransmission from one of the plurality of radios.
 7. The systemaccording to claim 1 wherein each of the plurality of radios includes anAM tuner, an FM tuner, and a satellite tuner for tuning AM radiostations, FM radio stations and satellite radio stations, said receiversystem determining which of the AM, FM and satellite stations of theplurality of the radio is tuned to.
 8. A system for providing anestimation of the number of radios tuned to each of a plurality ofdifferent radio stations, each of the radios transmitting one of aplurality of unique frequency signals based on which station that radiois tuned to, said system comprising: a plurality of bandpass filters,each filter passing the frequency signal of one of the unique frequencysignals transmitted from the plurality of radios; a plurality of powerdetectors, each of the power detectors receiving the frequency signalspassed by one of the band pass filters, said power detectors providing aseparate power measurement signal of the combined frequency signalsreceived by the system for each of the unique frequency signals; and aprocessor, said processor receiving the power measurement signals fromeach of the power detectors and providing an estimation of the number ofradios tuned to a particular radio station based on the powermeasurement signal for each unique frequency signal, the expected noiseof the system, and the expected received power for each signaltransmitted by the radios.
 9. The system according to claim 8 whereinthe system is positioned on a satellite orbiting the earth.
 10. Thesystem according to claim 8 wherein the processor provides an estimateof the number of radios transmitting each unique frequency signal basedon the power measurement signal for each unique frequency signal minusthe expected noise power in the system, and divided by the expectedreceived power from a single transmission from one of the plurality ofradios.
 11. The system according to claim 8 wherein each of theplurality of radios includes an AM tuner, an FM tuner, and a satellitetuner for tuning AM radio stations, FM radio stations and satelliteradio stations, said processor determining which of the AM, FM andsatellite stations each of the plurality of radios is tuned to.
 12. Thesystem according to claim 11 wherein each of the plurality of radiosfurther includes a carrier wave frequency determination system and acarrier wave generator, said carrier wave frequency system outputting aunique coded signal to the carrier wave generator depending on whichradio station the radio user selects, and said carrier wave generatorgenerating the unique frequency signal based on the coded signal fromthe carrier wave frequency system.
 13. A system for determining a stateof a plurality of transmitters, each transmitter transmitting one of aplurality of predefined signals based on the state of that transmitter,said system comprising a receiver system receiving the predefinedsignals, said receiver system separating the predefined signals intogroups of the same signal and measuring the combined power for eachgroup of separated signals, said receiver system determining the numberof transmitters transmitting each signal based on the combined power.14. The system according to claim 13 wherein the receiver systemprovides an estimate of a number of transmitters transmitting eachunique signal based on the combined power of each group of separatedsignals, the expected noise power in the receiver system, and theexpected received power from a single transmission from one of theplurality of transmitters.
 15. A method of identifying a state of aplurality of radios, said method comprising the steps of: providing aplurality of radios where each radio transmits one of a plurality ofunique signals based on the state of the particular radio; receiving theunique signals transmitted by the plurality of radios in a commonreceiver; separating the unique signals from the plurality of radiosinto groups in the receiver; measuring the combined power for each groupof separated unique signals; and determining the number of radiostransmitting each unique signal based on the combined power.
 16. Themethod according to claim 15 wherein the plurality of radios transmitunique signals based on what radio station each radio is currently tunedto.
 17. The method according to claim 15 wherein the step of determiningthe number of radios transmitting each unique signal includes providingan estimate of the number of the radios transmitting each unique signalbased on the combined power of each group, the expected noise power inthe receiver, and the expected received power from a single transmissionfrom one of the plurality of radios.